The invention relates to stuffer box methods for crimping polyester fibers. More particularly, the invention employs novel stuffer box geometry to produce crimped polyester fibers having substantially uniform primary and secondary crimps. In a preferred embodiment, the method results in polyester fibers, batting, fiberfill, yarn, carpet, and other improved products that are difficult, or even impossible, to produce by employing conventional polyester crimping procedures.
Conventional methods of producing crimped fibers using a stuffer box apparatus are well known, and generally include directing fibers between two driven rollers to force the fibers into a confined space (i.e., the stuffer box chamber). The stuffer box typically includes opposing doctor blades positioned close to a nip, which is formed by the two rollers. Side plates, and occasionally base plates as well, complete the crimping chamber. As the fibers are fed through the nip into the stuffer box chamber, the fibers accumulate, decelerate, and fold. The resulting fiber bends are referred to as xe2x80x9cprimaryxe2x80x9d crimps.
To facilitate the formation of primary crimps, a stuffer box is typically equipped with a flapper, which is located toward the back of the crimping chamber. An applied force moves the flapper deep into the crimping chamber, further restricting fiber movement through the stuffer box. This augments the forces exerted on the advancing fibers by the top and bottom doctor blades.
Exemplary stuffer box descriptions are set forth in U.S. Pat. Nos. 5,025,538; 3,353,222; 4,854,021; 5,020,198; 5,485,662; 4,503,593; 4,395,804; and 4,115,908. It will be understood, of course, that these patents provide a descriptive background to the invention rather than any limitation of it. The basic stuffer box design may be modified to include or exclude parts. Although by no means is this list of patents exhaustive, the disclosed patents nevertheless illustrate the basic stuffer box, structural elements.
Conventional crimping methods often fail to manipulate the stuffer box settings to produce fibers having substantially uniform primary and secondary crimps. This can result in fibers that demonstrate relatively poor crimp uniformity, and consequently variable and inconsistent fiber properties. As will be understood by those having quality control backgrounds, use of such inferior fibers in manufacturing certain products is undesirable.
For example, as a general matter, more crimps per unit length increases cohesion and, conversely, fewer crimps per unit length decreases cohesion. Depending on fiber use, cohesion may be advantageous (e.g., carding) or disadvantageous (e.g., fiberfilling). Regardless of the end use, fiber uniformity is beneficial because crimps per unit length may be maintained at a frequency that results in an optimal cohesion, whether high or low. In short, consistent fiber crimping means less deviation from the desired cohesion level. This promotes better quality control.
To the extent that the prior art discloses techniques to improve fiber crimp uniformity, the focus is exclusively upon ways to improve primary crimps. Nevertheless, fibers possessing regular primary crimps can fold into larger deformations as the fibers advance through the stuffer box chamber. These larger fiber deformations are referred to as xe2x80x9csecondary crimps.xe2x80x9d Each secondary crimp fold includes a plurality of primary crimp folds. The formation of secondary crimps depends, in part, upon the gap height between the doctor blades.
Conventional methods which recognize that secondary crimps can form within a common stuffer box apparatus nonetheless fail to teach or suggest regulating the fold dimensions of secondary crimps to provide desirable fiber properties. This is apparent by examining fibers that have emerged from a conventional stuffer box chamberxe2x80x94the step of the folds is usually non-uniform.
The present invention recognizes, however, that primary and secondary crimp uniformity reduces the variability of polyester fiber properties. Such quality control with respect to crimp uniformity improves the manufacturing operations that process polyester fibers. As will be understood by those with quality control experience, reducing manufacturing variability leads to better quality products. Therefore, a need exists for producing crimped fibers having substantially uniform primary and secondary crimps.
It is an object of the invention to produce polyester fibers having uniform primary and secondary crimps. It is a further object of the invention to produce such crimped polyester fibers by employing novel geometry within a longitudinal stuffer box chamber.
In a primary aspect, the invention is an improved method for processing polyester fibers through a stuffer box crimping apparatus. As used herein, xe2x80x9cpolyesterxe2x80x9d is any long-chain synthetic polymer composed of at least 85 percent by weight of an ester of a substituted aromatic carboxylic acid. The invention improves upon conventional stuffer box methods by narrowing the gap between the doctor blades and increasing the tip spacing (i.e., the distance between the doctor blade tips and the roller surface). This promotes the formation of substantially uniform primary and secondary crimps. Surprisingly, it also improves production throughput while improving fiber uniformity.
As a general matter, a gap between the doctor blades that is too narrow prevents the formation of secondary crimps. Conversely, a gap between the doctor blades that is too wide results in non-uniform primary and secondary crimps. The present method sets the stuffer box height as a function of fiber propertiesxe2x80x94particularly total denier per tow-band width. According to the Dictionary of Fiber and Textile Technology (Hoechst Celanese 1990), xe2x80x9ctotal denierxe2x80x9d is the denier of the tow before it is crimped, and is the product of denier per fiber and the number of fibers in the tow. Adhering to the relationship as herein disclosed maintains primary and secondary crimps in the advancing fibers that are substantially uniform, rather than irregular. In practice, the resulting crimp uniformity is demonstrated by the reduced movement of the flapper, which maintains a constant pressure upon the aggregation of fibers. The secondary crimp has predictable, not random, amplitude and percent. In general, xe2x80x9cpercent crimpxe2x80x9d refers to the length of a fiber segment after crimping divided by the length of the same fiber segment before crimping. It is believed that because the same longitudinal force produces the primary and secondary crimps, secondary crimp uniformity is a good indicator of primary crimp uniformity, and vice-versa.
In a second aspect, the invention is a polyester fiber product having uniform primary and secondary crimps. This crimp uniformity significantly reduces deviation with respect to fiber properties, such as cohesion, handling, and web strength (i.e., these properties become more predictable). It is believed that, all things being equal, crimp uniformity also increases breaking tenacity. Moreover, such uniformity increases the ability of a packaged, fiber aggregation to separate easily, sometime referred to as xe2x80x9copenability.xe2x80x9d The improved crimp in the crimped fiber also improves resistance to compression on a per weight basis, a most desirable characteristic for fiberfill. As will be understood by those of skill in the art, resistance to compression means the ability of a bulk of material to withstand an applied force without reduction.
In many instances, the user of crimped polyester fibers must sacrifice one desirable fiber property to achieve another. The present invention facilitates this by enabling the user of crimped polyester fibers to specify the properties of the crimped fibers within narrow limits and have such demands fulfilled. In conformance with well-understood quality control principles, minimizing crimp non-uniformity of polyester fibers facilitates the improved manufacture of products, such as batting and fiberfill.
The foregoing, as well as other objects and advantages of the invention and the manner in which the same are accomplished, is further specified within the following detailed description and the accompanying drawings, in which: